1. Field of Invention
The invention relates to an apparatus for controlling a driving force from a driving source, such as an engine of a vehicle having an automatic transmission.
2. Description of Related Art
A driver may apply pressure to the acceleration pedal to power on the engine when the transmission is shifted down based on a reduction of the vehicle speed as a result of a coasting down or a power-off. In this case, in the coast-down shift, the hydraulic pressure of a clutch for a high speed stage is released (released side hydraulic pressure) to reduce the torque capacity of the clutch, and the hydraulic pressure of a clutch for a low speed stage (engaged side hydraulic pressure) is increased by an upward corrective value at the time of the power-on but the clutch is kept in an unengaged state. In this state, the speed of rotation of the input shaft (turbine) continues decreasing toward a synchronization point of the low speed stage on the basis of the power-on state. The engine output is regulated at a constant opening of an electronic throttle regardless of loads, such as engine friction, the load of an air-conditioner, and electrical loads.
When the engine is powered on to increase the throttle opening immediately during a coast-down state in which the released side hydraulic pressure is decreased to release the clutch for the high speed stage and in which the increase of the engaged side hydraulic pressure has not reached an engaging pressure to leave the clutch for the low speed stage in a released state, the engine speed increases with the transmission system of the automatic transmission in a so-called free state, which can cause the engine to over-rotate. A shift shock can occur because the clutch for the low steed stage is engaged when the speed of rotation of the turbine has abruptly increased as a result of the over-rotation of the engine.
Even when the engine output is regulated as it is powered on to the constant throttle opening regardless of the loads, the absolute engine output becomes large if the actual loads are small to cause the engine to over-rotate. If the actual loads are great, the absolute engine output becomes small to cause a time lag because of a delay in synchronization.
For example, Japanese Patent Publication No. 59904/1995 has proposed an engine controller that detects the level of an increase in the number of rotations of a turbine during a downward shift and reduces an engine output when the level of the increase is equal to or greater than a predetermined value. However, this controller can be used only in a case in which the number of rotations of a turbine increases as a result of a downward shift and, when the engine is powered on in a coast-down state as described above, the rotation of the turbine reaches synchronization before the engaged side hydraulic pressure reaches an engaging pressure to cause the engine to over-rotate thereafter.
(1) The invention provides an engine controller for a vehicle having an engine and an automatic transmission for transmitting the rotation of an output shaft of the engine to an input shaft of the automatic transmission through a fluidic transmission device, changing the speed of rotation by connecting and disconnecting a plurality of engaging elements (clutches, brakes, and one-way clutches) to switch the path of transmission, and transmitting the rotation whose speed has been changed to the driving wheels, the automatic transmission controlling the engine during a coast-down to a predetermined gear stage (e.g., from a fourth gear to a third gear) by engaging an engaging element (e.g., an engaging element C-1) while releasing a predetermined engaging element (e.g., an engaging element B-1), wherein it has an engine speed detection unit for detecting the number of rotations of the engine output shaft; an input shaft speed detection unit for detecting the number of rotations of the input shaft; a power-on detection unit for detecting a power-on state caused by a driver; an engine output control unit for controlling the output of the engine; and an engine control unit for detecting the engine speed and the input shaft speed and outputting a signal to the engine output control unit such that a predetermined relationship is maintained between the engine speed and the input shaft speed when the power-on state is detected in the coast-down state.
The term xe2x80x9cenginexe2x80x9d represents a concept that means a driving source, and is not limited to internal combustion engines, such as gasoline engines and diesel engines, but implies other driving sources, such as electric motors. The fluidic transmission device may be a torque converter or a fluid coupling. Referring to the automatic transmission, it is preferable to use an automatic transmission that provides a plurality of transmission stages by engaging and releasing an engaging element, such as a clutch, a brake, or a one-way clutch, to switch a transmission path of a planetary gear device or parallel shaft gear device. However, this is not limiting the invention, and the term xe2x80x9cautomatic transmissionxe2x80x9d represents a concept that covers also other automatic transmissions, such as a synchronous engagement type transmission, that is, a multi-stage transmission shifted by an expert system using an actuator, such as a hydraulic cylinder. The engaging elements are not limited to frictional engaging elements, such as clutches and brakes, and one-way clutches are also implied by this term. Therefore, the coast-down is not limited to switching of an engaged clutch, i.e., so-called clutch-to-clutch switching, and engagement of a low speed stage with a one-way clutch is also implied by this term.
(2) The invention also provides an engine controller according to the above, in which the engine control unit outputs the signal to the engine output control unit such that a difference between the engine speed and the input shaft speed becomes constant.
(3) The invention provides an engine controller according to the above, in which the engine control unit outputs a signal to the engine output control unit such that the ratio between the engine speed and the input shaft speed becomes constant.
(4) The invention also provides an engine controller according to any of the above, in which the engine output is controlled such that the engine speed is higher than the input shaft speed in the coast-down state.
(5) The invention also provides an engine controller according to (2) above, in which a correction is made to reduce an amount of signal output to the engine output control unit when the difference between the engine speed and the input shaft speed is increased.
(6) The invention also provides an engine controller according to (2) above, in which a correction is made to increase the amount of signal output to the engine output control unit when the difference between the engine speed and the input shaft speed is reduced.
(7) The invention also provides an engine controller according to any of (1) to (6) above, in which the engine is an internal combustion engine; the engine output control unit is an electronic throttle; and the signal is a required throttle opening.
(8) The invention also provides an engine controller according to (7) above, in which the required throttle opening during the coast-down is a basic throttle opening normally required when the accelerator is totally closed; and the required throttle opening is obtained by adding an amount of regulation determined based on the difference between the engine speed and the input shaft speed to the basic required opening when the power-on state is detected.
(9) The invention also provides an engine controller according to (7) above, in which, when the required throttle opening is greater than the basic throttle opening normally required when the accelerator is totally closed, the required throttle opening, when the power-on state is detected, is obtained by adding an amount of regulation determined based on the difference between the engine speed and the input shaft speed that are based on the basic required throttle opening to the basic required throttle opening.
(10) The invention also provides an engine controller according to (7) above, in which when the required throttle opening is greater than the basic throttle opening normally required when the accelerator is totally closed and when there are great loads other than the vehicle load, the required throttle opening when the power-on state is detected is obtained by adding an amount of regulation determined based on the difference between the engine speed and the input shaft speed that are based on the basic required throttle opening to the required throttle opening that is greater than the basic required throttle opening.
(11) The invention also provides an engine controller according to any of (1) to (10) above, in which the engine control unit maintains the signal based on the engine speed and the input shaft speed until the input shaft speed is synchronized with the predetermined transmission stage (until a low gear synchronization point); and the engine output control unit sweeps up the same until it agrees with a throttle opening required by the driver.
According to (1) above, because the engine output is controlled such that a constant relationship is maintained between the engine speed and the input shaft speed when switching to the power-on state occurs during a coast-down, the over-rotation of the engine (over-rotation of the driving source) is prevented even when the automatic transmission is in a substantially free state, and a gear change can be smoothly made with a reduced shift shock and delay after the engaging element for the low speed stage is engaged.
According to (2) above, an engine can be controlled with high precision and reliability because an absolute engine output that is the total engine output minus an engine output based on the vehicle loads when the accelerator is totally closed, i.e., engine friction, electrical loads, and the load of an air-conditioner is accurately detected from the difference between the engine speed and the input shaft speed and because the engine output in the power-on state is regulated based on the absolute engine output.
According to (3) above, an engine can be controlled also based on the ratio between the engine speed and the input shaft speed.
According to (4) above, control is performed to keep the engine speed higher than the input shaft speed even during a coast-down, which allows a smooth transfer to engine control in the power-on state to prevent the over-rotation of the engine and a shift shock while preventing a shock attributable to switching between reverse driving and forward driving (tip-in).
According to (5) above, although an engine is likely to over-rotate when there is a great difference between the engine speed and the input shaft speed because of idle rotation, a correction is made to reduce the amount of operation of the engine output control unit, thereby making it possible to prevent the engine from over-rotating.
According to (6) above, although a gear change is likely to take time when the difference between the engine speed and the input shaft speed is small for causes that include great loads other than vehicle loads, such as the load of an air-conditioner, the amount of operation of the engine output control unit can be corrected to be large to prevent the occurrence of such a slow gear change.
According to (7) above, engine control can be properly performed in response to switching to the power-on state during a coast-down using an existing internal combustion engine and electronic throttle.
According to (8) above, an engine output is controlled by adding an amount of regulation determined by an absolute engine output based on the difference between the engine speed and the turbine speed to a basic throttle opening normally required when the accelerator is totally closed using an idling speed controller (ISC). This makes it possible to control an engine with high precision when switching to the power-on state occurs during a coast-down.
According to (9) above, an engine can be properly controlled without over-rotation using a proper required throttle opening when the throttle opening is greater than the normal basic required throttle opening as a result of idle rotation.
According to (10) above, an engine can be controlled based on a required throttle opening associated with idle rotation to prevent a slow gear change when there are great loads other than vehicle loads, such as a torque converter, even during idle rotation.
According to (11) above, the engine control based on the engine speed and the input shaft speed is maintained until a synchronization point of a low speed gear and swept up toward a throttle opening required by the driver, which allows a smooth downward shift to a low speed stage without causing the engine to over-rotate.